European Patent Publication EP 0,728,624 A2 relates to a method and apparatus for controlling an actuatable restraining device using predictive crash sensing. The predictive crash sensor, referred to herein as precrash sensor, is a radar system which detects targets located within a perimeter around the vehicle. The system determines three parameters, namely relative distance or target range, relative speed or target closing velocity and the angle of incidence. The trigger threshold is varied in response to at least one of these three parameters. The trigger threshold is compared with an acceleration integral or velocity signal referred to as a determined crash value which represents an estimated impact, but not an actual impact. Accordingly, the known vehicle occupant protection system is prone to a premature deployment of the restraining device. The known system can be triggered at lower acceleration or acceleration integral signals than is necessary or even safe. Further, the precrash sensors have proven to be prone to faults and are not suitable for all traffic situations. In particular, if the distances between the vehicle and the respective targets are very short for instance, when overtaking, when the lanes are narrow, or when driving along a crash barrier, or when unusual objects, for instance, a cardboard box or the like are present on the road, incorrect sensor evaluations may occur. In such a situation, the trigger threshold will be lowered so far that even a slight contact between both objects, a violent vehicle braking maneuver or even road vibrations may suffice to trigger the vehicle occupant protection device even when such triggering and deployment of the safety device is not yet needed for vehicle occupant protection. To the contrary, such premature deployment will obstruct the driver who will no longer be able to safely drive the vehicle in this hazardous situation, thus making a dangerous situation even more dangerous.
German Patent Publication DE 42 20 270 A1 discloses a vehicle occupant protection device that uses at least one acceleration sensor (11) and at least one deformation sensitive sensor (12). In the preferred embodiment at least two deformation sensitive sensors are arranged in a row for lateral impact detection. A signal processing unit (10) is provided which evaluates the signals from the deformation sensitive sensors which respond relatively early in the course of an impact, for providing a signal that reduces the response sensitivity of the at least one acceleration sensor in order to make it more sensitive. By arranging the two deformation sensitive sensors in a row, it is possible to gain information regarding the force and velocity of an impact when the spacing between the two sensors is known. A precrash signal as such is not employed according to this German Patent Publication DE 42 20 270 A1.
The two deformation-sensitive sensors may become active only when the impact actually occurs; therefore, they are impact or crash sensors and not precrash sensors, even though an "early warning function" can be implemented due to the spatially separate location of the sensor located closest to the exterior side of the vehicle. In addition to the "deviating sensor concept" in comparison to precrash sensors, the time interval between the signal from the outer crash sensor and the signal from the inwardly positioned crash sensor is much shorter than a time interval between signals from other sources such as precrash sensors. Therefore, precrash sensors offer significant safety benefits.
U.S. Pat. No. 5,285,188 (Yoshida) teaches processing a signal from a precrash sensor (11), referred to as a vehicle collision predicting unit and a signal from an impact sensor (30) for providing a collision signal. The two signals pass through an AND-gate to provide a trigger signal at the output of the AND-gate for the immediate deployment of the safety device when the distance between the two vehicles or an obstacle and the vehicle becomes zero within a predetermined time. A response threshold for the safety device trigger signal is not lowered.
German Patent Publication DE OS 43 24 753 A1 discloses a deployment mechanism for a safety device in a vehicle to protect passengers. Two sensors cooperate with each other for the deployment of a side air bag. A deformation or crash sensor is mounted either in the outer skin or directly behind the outer skin of the side of the vehicle body and a cross acceleration sensor is mounted centrally along the longitudinal vehicle axis. The evaluation of the signals from the deformation sensor or crash sensor starts the evaluation of the cross acceleration signal, whereby the response threshold is reduced to increase the sensitivity at the time of impact. The reduction of the threshold, or rather the increase of the sensitivity is made commensurate to the size of the deformation velocity. The combination of precrash signals with crash signals is not disclosed.
German Utility Model Publication G 92 15 383.6 discloses a sensor for evaluating optical signals that can be used for the present purposes. Similarly, European Patent Publication EP 0,763,724 A1 discloses a fiber optical load sensor suitable for the present purposes.